Oh no! At first I thought this paper was just bing silly/clever with `⟅⟆ : Bag` (it looks like a bag 💰 haha), but then I realised this is actually a thing! Unicode calls them 'bag delimiters'… 😱
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And so followed my first hunt for the history of a character's introduction into unicode: unicode.org/L2/L2003/03410 - no idea what the history is of these characters in mathematics though... 🤔
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Indeed I do. They were whiteboard notation in the Squiggol community in late 80s, early 90s. and I put them in the St Mary's Road symbol font. I guess Unicode picked them up from there.
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Exactly.
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Great! Looks super fascinating! Sadly the typesetters seemed not to have bag delimiters on hand in the 80s, scanning over those early papers.
Thanks and for playing your part in keeping this amusing typographic pun alive! 🥰👏